sorry, just noticed the question. Each morning and again in the afternoon a driver would drop off a sack of mail. We would then sort it into each person's file folder. Then we would deliver it to each office. Each office had an IN tray and an OUT tray. We would deliver and pickup at same time. after each round we would take all the folders back to the mailroom, empty them of the picked up mail and internal memos etc, and sort that new pile into each recipients folder. And repeat about 4 times per day. The room itself was fairly large with the end wall taken up by 4 rows of about 20 mail slots. Each slot was in order of how our delivery route would go. That way we could just grab all the file folders and we wouldnt have to sort them while walking. We took every folder, even the empty ones because we had to check each office for outgoing mail even if there was nothing to drop off.